As is well known in the art, video is displayed to a viewer by displaying a series of still frame images sequentially on a display. The images are displayed one after another at a rate that is fast enough so that it appears to the normal human eye that the movement of objects in the video is smooth and continuous. In digital video, each frame image is made up of pixels that each have a respective color intensity for each of the primary display colors (red, green, and blue). The digital value of each primary color intensity of the pixel is frequently defined by eight bits of data, allowing for definition of up to 255 levels of intensity for each color, and an eight-bit color depth of a possible 255×255×255=16,581,375 colors, ranging from black (0,0,0) to white (255, 255, 255).
In some digital video displays, especially LCD or liquid crystal on silicon (LCOS) displays, each still frame image of the video is in fact a series of one-color component frames, called bit planes, that are displayed in a series and add up to the total color frame image. In each bit plane, the pixels are either on or off, and those pixels that are on in the bit plane are all on in the same primary color and intensity.
Each bit plane corresponds to a respective bit in the set of digital data defining the color of the pixels. For example, in some systems, the first bit plane displayed corresponds to the most-significant bit of the red image for all of the pixels at the maximum red intensity for the display, then the next bit plane at half that red intensity for the next most significant red bit, etc., down to the last red bit plane corresponding to the least significant red bit, wherein all the pixels have a red intensity of 1/128 of the maximum red intensity. After the red planes, the green bit planes corresponding to the most significant to the least significant green pixel bits are similarly displayed, and then the blue bit planes.
The twenty-four bit planes are displayed so quickly that the total frame image display duration, i.e., the time from the start of the display of the first bit plane of the frame image to the end of the display of the last bit plane of that same frame, is less than the cycle time for display of each sequential image of the video, and the user normally sees only a moving video image, not individual bit planes or individual frame images.
In some environments, however, such as simulators for aircraft, bit-plane displays can be subject to some undesirable perception effects where the video being displayed has certain characteristics, or when the user's eyes pan or track across the image, so as to result in relatively rapid movement of the eye of the viewer relative to the objects seen in the displayed imagery.
In a simulator, usually there is a display that shows the user a real-time simulated out-the-window (“OTW”) view from the aircraft, and possibly other objects like simulated head-up display imagery, all of which are created by an image generating computer system to give realism to the simulation. The display frequently is a head-mounted display in which the user wears a helmet fitted with a visor and a head tracking apparatus. An image generator transmits digital video appropriate to the simulation and to the direction that the head tracker indicates the user is looking. If the user turns his head rapidly, the head tracker detects this, and the image generator makes the scene displayed on the visor move rapidly to one side or another to conform to the new point of view.
As the user turns his head, however, his eyes move more or less continuously across the field of view, i.e., across the field of objects visible in the display device. The video, in contrast to the continuous movement of the eye, is a series is a series of still color images, each of which is made up of a series of frames, each of which is made up of a subset of still bit-plane images in which virtual objects in the simulated video display, like a passing aircraft, or the entire field of view when the simulated ownship is rotating or moving, is displayed as essentially in one stationary location from the start of display of the first bit plane to the end of display of the last bit plane of the given frame image.
As illustrated in by FIG. 1, the effect of this on the user's eye moving continuously relative to the object is that the image of an object in early bit planes strikes the retina of the user's eye in a different location compared to its location in later bit planes of the same frame image, resulting in a perceived separation into the colors of the different bit planes, which degrades the realism of the simulation.
Rapid movement of various types may produce the problem of tracking of the eyes across the display to give rise to a perceived separation of the first and last bit planes. The usual source of the problem is rapid head rotation. In addition, though, ownship rotations in a simulation may give rise to tracking of the eye relative to the displayed image that creates the separation of bit planes, as may high-speed movement of an object relative to the ownship.